It is difficult to precisely determine what proportion of people with PHI experience symptoms, though this is reported to be in the range of 23-92% of infected individuals¹⁴. The presence of symptoms during PHI is predictive of long-term outcomes, with greater severity associated with more rapid disease progression^{15, 16}. Often these symptoms are non-specific in nature and may not be of sufficient severity for an affected individual to seek medical care, however severe illness leading to hospitalisation may be seen. The usual time from exposure to illness is 2-4 weeks^{17, 18}, though delayed seroconversion of up to 10 months has been observed¹⁹. Typically, the illness will be self-limiting, lasting approximately 3 weeks, however in up to 20% of cases, opportunistic infections can occur due to the transient lymphopenia of acute infection. Oral or oesophageal candidiasis is most common and Pneumocystis jirovecii pneumonia, cryptosporidiosis, herpes zoster and cytomegalovirus (CMV) disease have also been reported^{14, 20, 21}.

The originally described triad of symptoms associated with PHI includes fever, pharyngitis and lymphadenopathy. Fever is most common and is typically associated with headache and oral ulceration. Examination will typically reveal an erythematous and oedematous oropharynx without exudate. Painful mucocutaneous ulcers may also be seen, which may also be present in the oesophagus or anus or on the genitalia, with the important differential diagnosis being disease caused by co-existent sexually transmitted infections, such as ano-genital herpes or syphilis. Lymphadenopathy develops in the second week of illness, commonly involving the axillary and cervical nodes and tends to decrease in size following the acute presentation, however it may persist well after resolution of other symptoms. In the absence of fever, other symptoms may include myalgia, lethargy, rash, diarrhoea, and weight loss. Rarely, neurologic involvement can occur, in particular patients may present with aseptic meningitis, encephalopathy, myelopathy, or peripheral nervous system involvement^22-24.

It is important to consider co-infection with other viral, bacterial or fungal pathogens, which may complicate the clinical presentation. Co-infection with other viruses such as cytomegalovirus, hepatitis B or C viruses, herpes simplex virus or other sexually transmitted infections such as chlamydia, gonorrhoea or syphilis must be considered in the diagnostic work-up²⁵.